While China has just announced that it could make a vaccine against Covid-19 available from early November, a study published Tuesday, September 15 in the review Frontiers confirms what many researchers have been predicting for months: even with a vaccine, the coronavirus SARS-CoV-2 could, like the virus of influenza, become seasonal.
This study, taken up by L’Express , show that “The disease caused by the SARS-CoV-2 coronavirus will probably follow the same path as the other respiratory viruses: it will disappear in summer, but it will return in winter, at least in countries with a temperate climate”.
Researchers from the American University of Beirut’s Faculty of Medicine and Qatar University’s Biomedical Research Center, behind the study, believe “That the Covid-19 will cause several waves of epidemics until collective immunity is reached”, as Dr Hassan Zaraket points out. « The immunity produced by infection from all other coronaviruses is not eternal and, although the phenomenon still seems rare, there have been at least two cases of reinfection with Covid-19 documented so far ” he adds.
“In addition, we are not sure how effective the vaccines will produce or how long they will confer immunity, well, as an RNA virus SARS-CoV-2 is expected to evolve and , as mutations accumulate, the virus can escape the antibodies triggered by the vaccine and cause re-infections ” says the doctor.
In winter, temperate regions should be more affected
The virus respiratory systems, including coronaviruses, are generally more virulent in winter, especially in temperate countries. “We know that many respiratory viruses follow seasonal patterns, especially in temperate regions”, underlines Dr Hadi Yassine, from the University of Qatar, in Doha, co-author of the study. “Even though tropical regions like India or Brazil are severely affected, transmission of the virus has been more aggressive overall in temperate regions, indicating that cold and dry conditions favor SARS-CoV-2 infections. “, confide the two authors.
Other factors can also explain a resurgence of the virus in winter, such as greater promiscuity, since people are more likely to stay inside buildings because of the low temperatures.
The virus is expected to spread further throughout the year
However, the virus is not expected to become seasonal right away and is expected to continue to spread throughout the year. Its reproduction rate – the famous OR, which indicates the number of infections caused on average by an infected person – remains high. For a virus to be seasonal, its reproduction rate must be less than 1 in summer and greater than 1 in winter. However, today, the virus has a high RO (it is between 2 and 3, but some estimates place it rather close to 6).
“Most of the world’s population has not yet been confronted with Covid-19 and therefore has never developed adequate immune defenses”, explain the researchers. This summer the number of new cases increased sharply.